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Implemented promote mem->reg pass.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2005 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Cameron Buschardt 2002-03-27 23:17:37 +00:00
parent 2ba3a72c3a
commit 98a37c2b9c
1 changed files with 283 additions and 61 deletions
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344
lib/Transforms/Utils/PromoteMemoryToRegister.cpp
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@ -13,7 +13,7 @@
// Currently this just loops over all alloca instructions, looking for
// instructions that are only used in simple load and stores.
//
// After this, the code is transformed by...
// After this, the code is transformed by...something magical :)
//
//===----------------------------------------------------------------------===//
@ -24,90 +24,312 @@
#include "llvm/Method.h"
#include "llvm/BasicBlock.h"
#include "llvm/Assembly/Writer.h" // For debugging
#include "llvm/iPHINode.h"
#include "llvm/iTerminators.h"
using namespace std;
using cfg::DominanceFrontier;
// PromotePass - This class is implements the PromoteMemoryToRegister pass
//
//instance of the promoter -- to keep all the local method data.
// gets re-created for each method processed
class PromoteInstance
{
protected:
vector<AllocaInst*> Allocas; // the alloca instruction..
map<Instruction *, int> AllocaLookup; //reverse mapping of above
vector<vector<BasicBlock *> > WriteSets; // index corresponds to Allocas
vector<vector<BasicBlock *> > PhiNodes; // index corresponds to Allocas
vector<vector<Value *> > CurrentValue; //the current value stack
//list of instructions to remove at end of pass :)
vector<Instruction *> killlist;
set<BasicBlock *> visited; //the basic blocks we've already visited
map<BasicBlock *, vector<PHINode *> > new_phinodes; //the phinodes we're adding
void traverse(BasicBlock *f, BasicBlock * predecessor);
bool PromoteMethod(Method *M, DominanceFrontier & DF);
bool queuePhiNode(BasicBlock *bb, int alloca_index);
void findSafeAllocas(Method *M);
bool didchange;
public:
// I do this so that I can force the deconstruction of the local variables
PromoteInstance(Method *M, DominanceFrontier & DF)
{
didchange=PromoteMethod(M, DF);
}
//This returns whether the pass changes anything
operator bool () { return didchange; }
};
class PromotePass : public MethodPass {
public:
// runOnMethod - To run this pass, first we calculate the alloca instructions
// that are safe for promotion, then we promote each one.
//
virtual bool runOnMethod(Method *M) {
std::vector<AllocaInst*> Allocas;
findSafeAllocas(M, Allocas); // Calculate safe allocas
public:
// Get dominance frontier information...
DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
// Transform each alloca in turn...
for (std::vector<AllocaInst*>::iterator I = Allocas.begin(),
E = Allocas.end(); I != E; ++I)
promoteAlloca(*I, DF);
return !Allocas.empty();
}
// runOnMethod - To run this pass, first we calculate the alloca instructions
// that are safe for promotion, then we promote each one.
//
virtual bool runOnMethod(Method *M)
{
PromoteInstance inst(M, getAnalysis<DominanceFrontier>());
return (bool)inst;
}
// getAnalysisUsageInfo - We need dominance frontiers
//
virtual void getAnalysisUsageInfo(Pass::AnalysisSet &Requires,
Pass::AnalysisSet &Destroyed,
Pass::AnalysisSet &Provided) {
Requires.push_back(DominanceFrontier::ID);
}
private:
// findSafeAllocas - Find allocas that are safe to promote
//
void findSafeAllocas(Method *M, std::vector<AllocaInst*> &Allocas) const;
// promoteAlloca - Convert the use chain of an alloca instruction into
// register references.
//
void promoteAlloca(AllocaInst *AI, DominanceFrontier &DF);
// getAnalysisUsageInfo - We need dominance frontiers
//
virtual void getAnalysisUsageInfo(Pass::AnalysisSet &Requires,
Pass::AnalysisSet &Destroyed,
Pass::AnalysisSet &Provided) {
Requires.push_back(DominanceFrontier::ID);
}
};
// findSafeAllocas - Find allocas that are safe to promote
//
void PromotePass::findSafeAllocas(Method *M,
std::vector<AllocaInst*> &Allocas) const {
void PromoteInstance::findSafeAllocas(Method *M)
{
BasicBlock *BB = M->front(); // Get the entry node for the method
// Look at all instructions in the entry node
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(*I)) // Is it an alloca?
if (!AI->isArrayAllocation()) {
bool isSafe = true;
for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) { // Loop over all of the uses of the alloca
// Only allow nonindexed memory access instructions...
if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*UI)) {
if (MAI->hasIndices()) { isSafe = false; break; } // indexed?
} else {
isSafe = false; break; // Not a load or store?
}
}
bool isSafe = true;
for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) { // Loop over all of the uses of the alloca
if (isSafe) // If all checks pass, add alloca to safe list
Allocas.push_back(AI);
// Only allow nonindexed memory access instructions...
if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*UI)) {
if (MAI->hasIndices()) { // indexed?
// Allow the access if there is only one index and the index is zero.
if (*MAI->idx_begin() != ConstantUInt::get(Type::UIntTy, 0) ||
MAI->idx_begin()+1 != MAI->idx_end()) {
isSafe = false; break;
}
}
} else {
isSafe = false; break; // Not a load or store?
}
}
if (isSafe) // If all checks pass, add alloca to safe list
{
AllocaLookup[AI]=Allocas.size();
Allocas.push_back(AI);
}
}
}
// promoteAlloca - Convert the use chain of an alloca instruction into
// register references.
//
void PromotePass::promoteAlloca(AllocaInst *AI, DominanceFrontier &DFInfo) {
std::cerr << "TODO: Should process: " << AI;
}
// newPromoteMemoryToRegister - Provide an entry point to create this pass.
//
Pass *newPromoteMemoryToRegister() {
return new PromotePass();
return new PromotePass();
}
bool PromoteInstance::PromoteMethod(Method *M, DominanceFrontier & DF) {
// Calculate the set of safe allocas
findSafeAllocas(M);
// Add each alloca to the killlist
// note: killlist is destroyed MOST recently added to least recently.
killlist.assign(Allocas.begin(), Allocas.end());
// Calculate the set of write-locations for each alloca.
// this is analogous to counting the number of 'redefinitions' of each variable.
for (unsigned i = 0; i<Allocas.size(); ++i)
{
AllocaInst * AI = Allocas[i];
WriteSets.push_back(std::vector<BasicBlock *>()); //add a new set
for (Value::use_iterator U = AI->use_begin();U!=AI->use_end();++U)
{
if (MemAccessInst *MAI = dyn_cast<StoreInst>(*U)) {
WriteSets[i].push_back(MAI->getParent()); // jot down the basic-block it came from
}
}
}
// Compute the locations where PhiNodes need to be inserted
// look at the dominance frontier of EACH basic-block we have a write in
PhiNodes.resize(Allocas.size());
for (unsigned i = 0; i<Allocas.size(); ++i)
{
for (unsigned j = 0; j<WriteSets[i].size(); j++)
{
//look up the DF for this write, add it to PhiNodes
DominanceFrontier::const_iterator it = DF.find(WriteSets[i][j]);
DominanceFrontier::DomSetType s = (*it).second;
for (DominanceFrontier::DomSetType::iterator p = s.begin();p!=s.end(); ++p)
{
if (queuePhiNode((BasicBlock *)*p, i))
PhiNodes[i].push_back((BasicBlock *)*p);
}
}
// perform iterative step
for (unsigned k = 0; k<PhiNodes[i].size(); k++)
{
DominanceFrontier::const_iterator it = DF.find(PhiNodes[i][k]);
DominanceFrontier::DomSetType s = it->second;
for (DominanceFrontier::DomSetType::iterator p = s.begin(); p!=s.end(); ++p)
{
if (queuePhiNode((BasicBlock *)*p,i))
PhiNodes[i].push_back((BasicBlock*)*p);
}
}
}
// Walks all basic blocks in the method
// performing the SSA rename algorithm
// and inserting the phi nodes we marked as necessary
BasicBlock * f = M->front(); //get root basic-block
CurrentValue.push_back(vector<Value *>(Allocas.size()));
traverse(f, NULL); // there is no predecessor of the root node
// ** REMOVE EVERYTHING IN THE KILL-LIST **
// we need to kill 'uses' before root values
// so we should probably run through in reverse
for (vector<Instruction *>::reverse_iterator i = killlist.rbegin(); i!=killlist.rend(); ++i)
{
Instruction * r = *i;
BasicBlock * o = r->getParent();
//now go find..
BasicBlock::InstListType & l = o->getInstList();
o->getInstList().remove(r);
delete r;
}
return !Allocas.empty();
}
void PromoteInstance::traverse(BasicBlock *f, BasicBlock * predecessor)
{
vector<Value *> * tos = &CurrentValue.back(); //look at top-
//if this is a BB needing a phi node, lookup/create the phinode for
// each variable we need phinodes for.
map<BasicBlock *, vector<PHINode *> >::iterator nd = new_phinodes.find(f);
if (nd!=new_phinodes.end())
{
for (unsigned k = 0; k!=nd->second.size(); ++k)
if (nd->second[k])
{
//at this point we can assume that the array has phi nodes.. let's
// add the incoming data
if ((*tos)[k])
nd->second[k]->addIncoming((*tos)[k],predecessor);
//also note that the active variable IS designated by the phi node
(*tos)[k] = nd->second[k];
}
}
//don't revisit nodes
if (visited.find(f)!=visited.end())
return;
//mark as visited
visited.insert(f);
BasicBlock::iterator i = f->begin();
//keep track of the value of each variable we're watching.. how?
while(i!=f->end())
{
Instruction * inst = *i; //get the instruction
//is this a write/read?
if (LoadInst * LI = dyn_cast<LoadInst>(inst))
{
// This is a bit weird...
Value * ptr = LI->getPointerOperand(); //of type value
if (AllocaInst * srcinstr = dyn_cast<AllocaInst>(ptr))
{
map<Instruction *, int>::iterator ai = AllocaLookup.find(srcinstr);
if (ai!=AllocaLookup.end())
{
if (Value *r = (*tos)[ai->second])
{
//walk the use list of this load and replace
// all uses with r
LI->replaceAllUsesWith(r);
//now delete the instruction.. somehow..
killlist.push_back((Instruction *)LI);
}
}
}
}
else if (StoreInst * SI = dyn_cast<StoreInst>(inst))
{
// delete this instruction and mark the name as the
// current holder of the value
Value * ptr = SI->getPointerOperand(); //of type value
if (Instruction * srcinstr = dyn_cast<Instruction>(ptr))
{
map<Instruction *, int>::iterator ai = AllocaLookup.find(srcinstr);
if (ai!=AllocaLookup.end())
{
//what value were we writing?
Value * writeval = SI->getOperand(0);
//write down...
(*tos)[ai->second] = writeval;
//now delete it.. somehow?
killlist.push_back((Instruction *)SI);
}
}
}
else if (TerminatorInst * TI = dyn_cast<TerminatorInst>(inst))
{
// Recurse across our sucessors
for (unsigned i = 0; i!=TI->getNumSuccessors(); i++)
{
CurrentValue.push_back(CurrentValue.back());
traverse(TI->getSuccessor(i),f); //this node IS the predecessor
CurrentValue.pop_back();
}
}
i++;
}
}
// queues a phi-node to be added to a basic-block for a specific Alloca
// returns true if there wasn't already a phi-node for that variable
bool PromoteInstance::queuePhiNode(BasicBlock *bb, int i /*the alloca*/)
{
map<BasicBlock *, vector<PHINode *> >::iterator nd;
//look up the basic-block in question
nd = new_phinodes.find(bb);
//if the basic-block has no phi-nodes added, or at least none
//for the i'th alloca. then add.
if (nd==new_phinodes.end() || nd->second[i]==NULL)
{
//we're not added any phi nodes to this basicblock yet
// create the phi-node array.
if (nd==new_phinodes.end())
{
new_phinodes[bb] = vector<PHINode *>(Allocas.size());
nd = new_phinodes.find(bb);
}
//find the type the alloca returns
const PointerType * pt = Allocas[i]->getType();
//create a phi-node using the DEREFERENCED type
PHINode * ph = new PHINode(pt->getElementType(), Allocas[i]->getName()+".mem2reg");
nd->second[i] = ph;
//add the phi-node to the basic-block
bb->getInstList().push_front(ph);
return true;
}
return false;
}